Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
irregular [ɪˈrɛgjulər] adj (surface) неро́вный*неро́вен (pattern) непра́вильной фо́рмы; (action, event) нерегуля́рный*нерегуля́рен (behaviour) распу́щенный; (LING) (verb etc) непра́вильный
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.